1. Field of the Invention
The present invention concerns a thermoplastic polymer composition excellent in melt adhesion, a laminate structure having a layer of the thermoplastic polymer composition and a layer comprising other material, as well as a manufacturing method thereof.
More in particular, the present invention relates to a thermoplastic polymer composition excellent in flexibility, elasticity, mechanical property, oil resistance and moldability, capable of adhering strongly under melting with various kind of materials, and capable of simply and smoothly manufacturing various laminate structures or composite articles having a layer of the thermoplastic polymer composition and a layer comprising such materials by melt adhesion, as well as a laminate structure having a layer of the thermoplastic polymer composition and a layer of other material, and a manufacturing method thereof.
2. Description of the Prior Art
Heretofore, products such as films, sheets, and molding products have been manufactured generally by using high molecular polymers, but use of a single polymer alone often results in poor moldability or cannot provide properties conforming the application uses, depending on the kind of the polymer, application use of products or purpose of use. In view of the above, it has been attempted to enhance the moldability or improve the mechanical property or chemical property of resultant products by using a polymer composition comprising two or more of polymers in a blend or in the form of laminates. However, when different kinds of polymers are blended into a polymer composition, combinations showing satisfactory compatibility are not present by so much purpose which cannot often be attained in view of inhomogenity caused by poor compatibility and interlayer separation.
Block copolymers comprising a styrene polymer block and a diene polymer block (hereinafter sometimes referred to as "styrene-diene block copolymer") and hydrogenation products thereof have rubber elasticity at a normal temperature and can be molded easily in a plasticated and molten state under heating, and are excellent in the balance between the flexibility and the mechanical property, so that they have been used generally in various fields as a sort of so-called thermoplastic elastomers in recent years.
As one of typical application uses of them, there can be mentioned a laminate structure (composite products) having a layer of a styrene-diene block copolymer and/or hydrogenation product thereof and a layer of a plastic and/or metal layer. A synthetic resins such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyvinyl chloride, polyvinylidene chloride, polystyrene, impact resistant polystyrene, ABS resin, polyethylene terephthalate, nylon and polycarbonate are used as the plastic layer in the laminate structure described above. Further, use of various metals such as stainless steel, iron, aluminum, copper, tin-plated or zinc galvanized steel has been attempted as the metal layer in the laminate structure.
In the laminate structures described above, the layer of the styrene-diene block copolymer and/or hydrogenation product thereof is flexible, gives good feeling upon contact and has properties such as excellent elasticity, vibration damping, sound damping, cushioning effect and rupture preventive function, while the layer of the synthetic resin or metal has a shape retaining function, reinforcing effect and fixing function. Therefore, the laminate structures have been noted in recent years as a high value-added products and the use of them has been attempted for various products as sheets, films and in the form of various molding products having complicate shapes, for example, as various kinds of parts for automobiles or vehicles such as instrument panels, center console boxes, door trims, pillars and assist grips; building materials such as doors and window frames, various switches or knobs in electric products and medical gypsum.
However, since the styrene-diene block copolymers and hydrogenation products thereof are less polar materials and, accordingly, they can be melt-adhered or integrally melt molded with identical kind of less polar plastics but their melt adhesion with highly polar plastics or metals is difficult. Therefore, in a case of compositing them by lamination with highly polar materials, there has been adopted a mechanical bonding method such as a method of providing an engaging portion (fitting portion) such as unevenness to a member (layer) comprising a styrene-diene block copolymer or a hydrogenation product thereof, and to a member (layer) comprising a plastic or metal and engaging (fitting) to join them or using another joining method, or a joining method using an adhesive.
However, since the method of providing the engagement such as unevenness makes the structure of a molding die for forming each of members complicate, it takes much time and labors for the manufacture of the die or increases the cost and, in addition, requires a complicate operation of engaging (fitting) both of the members.
The method of using the adhesive makes the step complicate in that both of the members are bonded by using the adhesive during or after the manufacture of both of the members. In addition, the adhesive used not always has high adhesion to both of the materials and results in a problem in view of adhesion failure, and the durability of adhesion strength and water resistance. Moreover, the organic solvent used for the adhesive gives a problem of worsening the working circumstance or ecological environment.
On the other hand, thermoplastic polyurethane elastomers having excellent abrasion resistance and oil resistance, rubber elasticity and melt moldability, have been used for various application uses including hoses, belts and tubes. However, since the thermoplastic polyurethane elastomers are poor in the hot water resistance and weather proofness, there range of application use is restricted at present.
Japanese Patent Unexamined Publication Sho 52-150464 and British Patent No. 1581167 describes a composition in which an engineering thermoplastic resin having predetermined properties is blended with a styrene-diene block copolymer and/or hydrogenation product thereof, and the publication discloses that the composition is suitable, particularly, to insulators for conductors and soldering wires and that thermoplastic polyurethane is used as a sort of the engineering thermoplastic resins described above. However, since the styrene-diene block copolymer and the thermoplastic polyurethane are poor in compatibility, properties of both of the polymers cannot be provided sufficiently, failing to obtain a useful polymer composition.
Further, various proposals have been made so far for the techniques with an aim of improving the melt-processability of the styrene-diene block copolymer or a hydrogenation product thereof, and a melt-processable composition comprising a styrene-diene block copolymer or a hydrogenation product thereof blended with a thermoplastic urethane elastomer has been known as such a prior art (Japanese Patent Unexamined Publication Hei 6-107898, U.S. Pat. No. 5,472,782 and Japanese Patent Unexamined Publication Hei 8-72204). However, use of the melt-processable composition sometimes results in a problem of failing to obtain a sufficient bonding strength or the lack of the durability of the adhesion strength depending on the kind of the material laminated therewith. Moreover, compatibility (melt dispersibility) between the styrene-diene copolymer or hydrogenation product thereof and the polyurethane thermoplastic elastomer in the melt-processable composition is not quite satisfactory, so that the composition shows no good mechanical properties and results in a problem such as delamination or unstability of adhesion strength in the lamination molded products obtained, for example, by composite layer injection molding.
Modification of a styrene-diene block copolymer with an unsaturated carboxylic acid or a derivative thereof and blending with a thermoplastic polyurethane elastomer has been proposed with an aim of improving the compatibility between the styrene-diene block copolymer and the thermoplastic polyurethane elastomer has been proposed (Japanese Patent Unexamined Publication Sho 63-254156). However, the thus obtained polymer composition involves a problem in view of the moldability and, in addition, the kind of the materials to melt adhesion therewith is restricted, shows no melt adhesion with various materials and has a drawback that the surface roughness is large for the molding products obtained from the polymer composition.
Further, it has been also known to add a styrene-diene block polymer modified with an unsaturated dicarboxylic acid or a derivative thereof as a compatibilizing agent to a polymer composition comprising a styrene-diene copolymer and a thermoplastic polyurethane elastomer (Japanese Patent Unexamined Publication Sho 56-115352 and U.S. Pat. No. 4,429,076). However, it cannot be said that sufficient improving effect can be obtained also in this case like that the cases described previously.